linux-kernel - Re: [PATCH] mm: check pfn_valid first in zero_resv

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Message-ID: <20171201092951.GA2943@dhcp-128-65.nay.redhat.com>
Date:   Fri, 1 Dec 2017 17:29:51 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, pasha.tatashin@...cle.com,
        linux-mm@...ck.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] mm: check pfn_valid first in zero_resv_unavail

On 12/01/17 at 10:19am, Michal Hocko wrote:
> On Fri 01-12-17 16:56:57, Dave Young wrote:
> > On 11/30/17 at 10:35am, Michal Hocko wrote:
> [...]
> > > Can we exclude that range from the memblock allocator instead? E.g. what
> > > happens if somebody allocates from that range?
> > 
> > It is a EFI BGRT image buffer provided by firmware, they are reserved
> > always and can not be used to allocate memory.
> 
> Hmm, I see but I was actually suggesting to remove this range from the
> memblock allocator altogether (memblock_remove) as it shouldn't be there
> in the first place.

Oh, I'm not sure because it is introduced as a way for efi to reserve
boot services areas to be persistent across kexec reboot. See
drivers/firmware/efi/efi.c: efi_mem_reserve(), BGRT is only one user
of it, there is esrt and maybe other users, I do not know if it is safe
:(

> -- 
> Michal Hocko
> SUSE Labs

Thanks
Dave